Microphone



Nov. 28, 1939.

w. H. HUTH mcnornoua Filed Aug. 30,, 1.937

liliiiiiiii/IiI/Ii/i III/ Patented Nov. 28, 1939 f umrao sra'rss art sts PATENT or ies MICROPHONE Walter H. Hath, Chicago, Ill., assignor to Aurcx Corporation, Chicago, 111., a corporation of II- linois Application August 30, 1937, Serial No. 161,56

"J Claims. (Cl. 179-443),

acterized by roughness or irregularity, so that fiexion of one surface away from the other, while maintaining a fixed minimum contact between them ata certain point, will vary the resistance of the microphone circuit in which the instrument is included.

It. is also an objectto provide a novel and improved construction and arrangement whereby the variable resistance comprises two or more engaging surfaces, formed to microscopically fit each other at only a few-spots on said surfaces, either fiatwise or by use of surfaces characterized by roughness, orirregularity, so that the very slightest movement toward separation or closure at any of those spots would cause a considerable change in the area of contact.

Another object isto provide certain details and features of construction tending to increase the general efl iciencyand the desirability of a microphone of this particular character.

To these and other useful ends, the invention consists in matters hereinafter set forth and claimed, and shown in the accompanying drawing, in which Fig. 1 is a diagrammatic sectional view showing a microphone embodying the principles'of the invention.

Fig. 2 is a similar view showing another form of the invention.

Fig. 3 is a similar view showing a different form of the invention.

tain suitable minimum of contact between them, providing the maximum degree of resistance in the variable resistance thus provided in any transmitting circuit in which the instrument is included. Sound vibrations impinging on the diaphragm I or the diaphragm 3 will obviously vibrate them and cause the area of contact between the surfaces 2 and 5 to vary rapidly, thus setting up a pulsating or Variable current in the transmission circuit. The screw 4 can be adjusted to regulate the tension of the member 3 of the instrument.

In Fig. 2, the structure is similar to that described, but in this case the middle portions of the two coated diaphragms are clamped together by a screw and nut device I, and two or more adjusting screws 8 are provided, so that the variable resistance'is between the middle and the periphery of the diaphragms.

In Fig. 3, the construction is similar, but in this case a sound diaphragm 9 isconnected by a rod it with the movable one of the two coated plates or members, to cause the resistance between the latter to vary.

In Fig. 4, the construction is likethat shown in Fig. 1, but in this case the surfaces are corrugated or wavy, as at H, to illustrate how the engaging surfaces may be irregular but still fit accurately and minutely together, either all over or at a few spots on the surfaces.

Thus in each form of the invention there is a pair of engaging resistance surfaces that are formed to have a microscopic all-over or substantially all-over engagement with each other. The surfaces can be optically fiat, so to speak, or substantially optically fiat, in which case each would be a duplicate of the other. If desired, the two surfaces can be curved or rough or irregular, in which case each surface will exactly fit the other to form a voidless joint between them when they are tight together, as each will have a microscopic fit with the other. Thus there is a variable re sistance between two flexible films or coatings, in each form of the invention, each coating having a separable contact with the other, except where they are held normally in contact with each other. The fixed minimum conductivity tween the two. surfaces may also be accomplished by other means than contact, such as 2. connecting and conducting element.

stances might be rendered flexible and suitable for the purpose, as the invention contemplates two or more conducting surfaces having a variable area of contact between them while either one or both of them are vibrating. It will be understood, of course, that there can be more than one pair of the conducting surfaces.

There might be only one coating, and in addition two surfaces might be fitted together by hydraulic pressure, but there are various ways of insuring an, exact microscopic fit between the conducting surfaces, and the invention is not limited to any particular method, although some of the methods will be described more in detail as follows:

(1) By breaking a piece of material apart so that the broken surfaces when placed together will absolutely fit all over.

(2) By having two optically flat surfaces, or substantially optically flat surfaces, which will provide a tight fit all over, or substantially all over.

(3) By having one surface of a plastic nature and pouring it on to conform to the other surface, then taking it off again, and later putting it back on the other surface. That will provide a very tight fit, so close that very slight separation or closure will cause quite a large change in the area of contact.

(4) By compressing two surfaces together hydraulically, with or without heat, so that the metal or other substance will be caused to flow and the surfaces will thus conform absolutely to each other, so that the very slightest movement of one surface toward separation or closure will cause a very large change in the area of contact.

It will be understood that the surfaces that are placed together may only touch in a few spots, and in such case, of course, the electricity would be conducted only through those few spots, but the fit will be very tight, and even the very slightest movement toward separation or closure at any of those spots will cause a considerable change in the area of contact.

Thus it will be seen that the invention consists of a very sensitive instrument, so that a very slight motion between the two surfaces will make a very great change in the area of contact, which gives a wide range of resistance and greater efficiency in the microphone.

From the foregoing, it will be seen that the contact between the two elements is very delicate, and that the instrument is very sensitive, as any slight disturbance results in a considerable variation in contact between the elements, with a consequent wide fluctuation of the resistance of the microphone circuit. For that purpose, as shown, the normal contact may be the minimum, so that the resistance Varies between that and the maximum that results when the two surfaces are entirely in contact with each other. Obviously, however, the normal condition may be the maximum contact, in which case the microscopic or optical fit would be the normal condition. But, as shown, the said fit is only co-extensive with the two surfaces when the acoustical disturbance is suflicient to bring both surfaces entirely together, so that the resistance in the circuit is reduced to a minimum. Hence the invention contemplates one or more conducting surfaces having a perfect superficial fit, but the maximum contact of such fit may be either the normal or the abnormal condition of the instrument. One surface is preferably metallic, but the co-operating surface may be rigid and non-metallic. The sensitivity thus obtained from the resistance surface is very great.

Thus it will be seen that the two engaging or contacting surfaces are connected in series in the instrument circuit, as shown in Fig. 5 of the drawing, so that each is always entirely in said circuit. Also, in each form of the invention one surface is normally curved toward the other. In Fig. 1 the flexible and vibratory surface is nor mally fiat, but the stationary surface is curved toward the vibratory surface. In Fig. 2 the vibratory surface is flat, and the fixed surface is normally curved toward the vibratory surface. In Fig. 3 the fixed surface is flat, and the vibratory surface is normally curved toward the stationary surface. In Fig. 4 each surface is normally curved toward the other, and in addition each surface is normally curved away from the other. In addition, in Fig. 4, it will be seen that the lower surface has an over-all curve toward the other surface, as the lower member is gradually curved downwardly at its right hand end. In this way, with the two electrode surfaces included in series in the instrument circuit,'each surface is always entirely in said circuit, as described and indicated, which means that as the two surfaces separate each film of metal has the greater portion thereof out of contact with the other, and is still included in said circuit.

Thus two electrodes are preferably connected in series, as indicated in Fig. 5 of the drawing, in each form of the invention, and the two electrode surfaces may be counterparts. of each other, or they may be rough or irregular interfitting surfaces, depending upon whether they are smooth or uneven. In any event, in each form of the invention, there is exact conformity between the two electrode surfaces, as each is shaped to conform absolutely to the other, when the two surfaces are tightly and entirely together. The two opposing surfaces of the two electrodes are normally in contact with each other, andare in series in the instrument circuit, so that complete separation of the two surfaces would open the circuit. Therefore, in effect, the resistance of this circuit is varied by alternately opening and closing the circuit, so to speak, for while it is never completely opened, the movement of one electrode away from the other is in effect an attempt to open the circuit, and as this opening movement increases, the resistance of the circuit is increased, and with the two electrodes completely separated, the circuit would be absolutely open. In that sense, therefore, the resistance is varied by alternately opening and closing the circuit, inasmuch as the separation of the two electrodes, if carried far enough, would absolutely open the circuit. But in actual operation, the circuit is normally and at all times closed, inasmuch as the two electrodes normally engage each other, and in actual use may have only a minimum of contact with each other, alternating with periods of maximum contact with each other.

The important aspect of the invention, however, it will be seen, is that each surface conforms absolutely and minutely to the other, and this may be done either by a perfectly smooth, flat, optical fit, or by means of rough or irregular interfitting surfaces, so that the important feature of the invention is in the relative formation between the two opposing electrode surfaces.

The vital thing, therefore, resulting from the absolute or at least microscopic fit between the engaging Surfaces of the electrodes, or the absolute or practically absolute conformity of one surface to the other, in one way or another, is that there is the greatest possible change in resistance with a minimum amount of motion. In other words, if the fit is not absolute or at least microscopic, then there is necessarily more motion, and the advantage of the absolute fit, or practical conformity of one surface to the other, which is of the essence of the invention, is not obtained.

Obviously, the effect of having each electrode surface an exact and absolute counterpart of the other, or each irregular and exactly fitting the other to form a. voidless joint between them when they are tight together, is that there is an exact and absolute fit between them when they meet, so that when pressed together no 'space will exist anywhere between them.

.The invention, therefore, obviously contemplates a microphone instrument that will require but very little electric power, and that Will involve practically only a minimum of motion, in order to provide a highly sensitive instrument of this kind.

What I claim as my invention is: 1. In a microphone instrument a pair of resistance surfaces forming relatively movable electrodes in the circuit of the instrument, each surface conforming to the other so as to make an optical fit, at least one electrode having its surface formed by a thin metal coating, and means to vibrate the electrodes relatively to each other, to vary the contact between them, and thereby vary the resistance of said circuit. I

2. A structure as specified in claim 1, said surfaces being irregular and exactly fitting each other to form a voidless joint between them when they are tight together.

3. A structure as specified in claim 1, said surfaces'being smooth and fiat and exact duplicates or counterparts of each other. v

4. A structure as specified in claim 1, said surfaces being smooth and curved.

5. A structure as specified in claim 1, said surfaces being flexible. 

